title: Intrinsically disordered and aggregation prone regions underlie β-aggregation in S100 proteins.
abstract: S100 proteins are small dimeric calcium-binding proteins which control cell cycle, growth and differentiation via interactions with different target proteins. Intrinsic disorder is a hallmark among many signaling proteins and S100 proteins have been proposed to contain disorder-prone regions. Interestingly, some S100 proteins also form amyloids: S100A8/A9 forms fibrils in prostatic inclusions and S100A6 fibrillates in vitro and seeds SOD1 aggregation. Here we report a study designed to investigate whether β-aggregation is a feature extensive to more members of S100 family. In silico analysis of seven human S100 proteins revealed a direct correlation between aggregation and intrinsic disorder propensity scores, suggesting a relationship between these two independent properties. Averaged position-specific analysis and structural mapping showed that disorder-prone segments are contiguous to aggregation-prone regions and that whereas disorder is prominent on the hinge and target protein-interaction regions, segments with high aggregation propensity are found in ordered regions within the dimer interface. Acidic conditions likely destabilize the seven S100 studied by decreasing the shielding of aggregation-prone regions afforded by the quaternary structure. In agreement with the in silico analysis, hydrophobic moieties become accessible as indicated by strong ANS fluorescence. ATR-FTIR spectra support a structural inter-conversion from α-helices to intermolecular β-sheets, and prompt ThT-binding takes place with no noticeable lag phase. Dot blot analysis using amyloid conformational antibodies denotes a high diversity of conformers; subsequent analysis by TEM shows fibrils as dominant species. Altogether, our data suggests that β-aggregation and disorder-propensity are related properties in S100 proteins, and that the onset of aggregation is likely triggered by loss of protective tertiary and quaternary interactions.
authors.affiliation: Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: Sofia B
authors.initials: SB
authors.lastname: Carvalho
authors.forename: Hugo M
authors.initials: HM
authors.lastname: Botelho
authors.forename: Sónia S
authors.initials: SS
authors.lastname: Leal
authors.forename: Isabel
authors.initials: I
authors.lastname: Cardoso
authors.forename: Günter
authors.initials: G
authors.lastname: Fritz
authors.forename: Cláudio M
authors.initials: CM
authors.lastname: Gomes
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D005427:Flocculation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D017510:Protein Folding; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D009418:S100 Proteins / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D011994:Recombinant Proteins; D009418:S100 Proteins